Problems caused by the volcano prompted the extra trip
An extra weekend ferry trip between Shetland and Aberdeen was put on due to the flight problems caused by the Iceland volcano.
NorthLink said there had been "unprecedented, last-minute demand for places" on its ferry Hrossey.
It left Lerwick on Friday night for a Saturday morning Aberdeen arrival.
It was decided Hrossey would then go back to Lerwick, arriving on Saturday night, and then return to Aberdeen, arriving on Sunday morning.
The plan was implemented as the next original timetabled northbound service would not have been until Sunday night.
Hrossey then reverted to scheduled service, with a 1700 BST northbound departure from Aberdeen on Sunday.
NorthLink chief executive Bill Davidson said: "The air restrictions imposed due to the volcanic ash have meant we've seen unprecedented last-minute demand for our services.
"Our customer service centre has never seen such a high rate of calls.
"Our staff have worked extremely hard to help all passengers and the extra sailings will help to ease the pressure which has been made even more challenging because we have one of our vessels away for annual refit."
He added: "We have been in regular contact with the Scottish government as the volcanic ash problem has developed and they have agreed to our suggestion of operating the extra services on Saturday."
Shetland Islands Council welcomed the extra sailing.
Convener Sandy Cluness said: "We have been keeping in regular contact throughout this disruption and it is good to see that the Scottish government and Northlink are taking prompt action to help maintain the vital lifeline links to Shetland."